It is known to attach an artificial foot to a lower leg part of a patient such that the foot structure manages without a joint in the region of the natural ankle joint. The flexing action of the foot during walking is accomplished by corresponding elastic formations of the foot structure.
U.S. Pat. No. 5,993,488 discloses a foot structure which includes an upper connection plate, an ankle plate connected solidly to the connection plate and a somewhat bulged sole plate. At the same time the sole plate has approximately the length of the artificial foot and is flexible in a longitudinal direction. The ankle plate is designed shorter and lies substantially parallel to the sole plate. Situated between the ankle plate and the sole plate is a foam block made of relatively firm, though elastic, foam. The foam block has a cross-sectional area for a horizontal cut which corresponds approximately to the cross-sectional area of the ankle plate so that the foam block fills out the interstice between the ankle plate and the sole plate over the entire size of the ankle plate. The parts are connected to one another by adhesion and are secured against delaminating by a band looped around the sole plate and the ankle plate with the interposed foam block. This foot structure causes compression of the foam block, resulting in a shift of the force transfer from the ankle plate to the sole plate correspondingly with the displacement of weight from rear to front. This can be meaningful for a user's gait, and particularly for heel-toe walking on the foot. However it may lead to an unsteady feeling when standing if slight displacements in weight lead to corresponding displacements of the introduction of force between the ankle plate and the sole plate. This gives the patient an unsteady “wobbly” feeling, since there is no defined point for introducing weight forces to the foot construction. This also applies for lateral displacements of weight and for displacements of weight in intermediate directions oblique to the longitudinal axis of the foot.
U.S. Pat. No. 4,446,580 discloses a foot construction in which a tubular lower leg part is connected to a base plate via a hinge joint offset forwards with respect to its longitudinal axis. The lower leg part is guided relative to a guide rod attached flexibly to the base plate, whereby the pivoting motion of the lower leg part around the hinge joint in the base plate is damped by means of plastic dampers. The base plate is solidly anchored in a recess of a sturdy artificial foot. An elastically springloaded sole structure and heel strike damping connected thereto are not provided.